From c1f2d450188627dd0d53280571e0c5550c73bcf4 Mon Sep 17 00:00:00 2001
From: nsz <nsz@port70.net>
Date: Sun, 25 Sep 2011 18:36:22 +0200
Subject: [PATCH 1/1] vmfill: portable way to manage the size of the available
 vm

---
 vmfill.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 vmfill.c

diff --git a/vmfill.c b/vmfill.c
new file mode 100644
index 0000000..a7f0a15
--- /dev/null
+++ b/vmfill.c
@@ -0,0 +1,71 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#ifndef PAGE_SIZE
+	#define PAGE_SIZE sysconf(_SC_PAGE_SIZE)
+#endif
+
+static void printvm() {
+	int fd = open("/proc/self/smaps", O_RDONLY);
+	char buf[4096];
+	int n;
+
+	printf("/proc/self/smaps:\n");
+	fflush(stdout);
+	while ((n = read(fd, buf, sizeof buf)) > 0)
+		write(1, buf, n);
+	close(fd);
+}
+
+static size_t mmapmax(int fd, void **p) {
+	size_t i,j,n=0;
+
+	for (i=j=SIZE_MAX/2+1; i>=PAGE_SIZE; i/=2) {
+		if ((*p=mmap(NULL, j, PROT_NONE, MAP_PRIVATE, fd, 0)) == MAP_FAILED)
+			j -= i/2;
+		else {
+			n = j;
+			munmap(*p, n);
+			j += i/2;
+		}
+	}
+	if (n && (*p=mmap(NULL, n, PROT_NONE, MAP_PRIVATE, fd, 0)) == MAP_FAILED) {
+		fprintf(stderr, "failed to mmap the same amount again.\n");
+		exit(1);
+	}
+	return n;
+}
+
+int main(int argc, char *argv[]) {
+	const int fd = open("/dev/zero", O_RDWR);
+	void *p[100];
+	size_t n[100];
+	size_t sum = 0;
+	int i;
+	int vmmaps = 0;
+
+	if (argc == 2 && argv[1][0]=='-' && argv[1][1]=='v')
+		vmmaps = 1;
+
+	for (i=0; i<sizeof p/sizeof *p; i++) {
+		n[i] = mmapmax(fd, p+i);
+		if (!n[i])
+			break;
+		sum += n[i];
+		printf("%d %16zu B %012zx-%012zx\n", i, n[i], (size_t)p[i], (size_t)p[i]+n[i]);
+	}
+	printf("mmaped %zu B in %d blocks.\n", sum, i);
+
+	printf("try malloc:");
+	for(i=0; i < 1000 && malloc(PAGE_SIZE) != NULL; i++)
+		printf(".");
+	printf(" %zu B\n", i*(size_t)PAGE_SIZE);
+
+	if (vmmaps)
+		printvm();
+	return 0;
+}
-- 
2.20.1